(CNN) - Controversy continues to swirl around New Jersey Sen. Robert Menendez - including his relationship with a generous Democratic donor whose plane he took to the Dominican Republic and who has business ties in that Caribbean nation.

Menendez first came under scrutiny shortly before Election Day last fall, when a conservative online publication cited three unidentified sources who claimed the senator had flown on private planes to the Caribbean and during the trip had sex parties with prostitutes.